1. Field of the Invention
The present invention relates generally to medical devices, and more particularly to an improved multi-lumen catheter.
2. Description of Related Art
Multi-lumen catheters are used for a variety of applications where it is necessary to have two or more separate fluid pathways. One such application for a multi-lumen catheter is for use in hemodialysis. During hemodialysis, a dual-lumen catheter can be employed to simultaneously accommodate opposing blood flow. More specifically, one lumen carries blood from a patient to a dialysis machine where it is processed for the removal of toxins, while the opposing lumen returns the purified blood to the patient.
Multi-lumen catheters are well known in the art. Dual lumen catheters, incorporating parallel D-shaped lumen to separate the blood flow and increase the rate of blood flow both into and out of the body, improved upon the use of multiple single lumen catheters. Subsequently, a third circular lumen was introduced to the dual lumen catheters to provide an additional inlet/outlet. Such a catheter can be seen in U.S. Pat. No. 5,797,869 to Martin. In Martin, the third lumen is located in the center of the internal septum, between the two semi-circular lumen. This configuration is intended to give the physician the option of simultaneously injecting a liquid medication during the dialysis procedure, an option not available with a simple dual lumen. However, locating a central lumen between the blood-carrying lumen compromises the reliability of blood flow. Another disadvantage in the catheters of the type described in Martin is that the inlet and outlet openings of the lumen are in close proximity to one another so that toxic blood and purified blood can mix, reducing the efficiency of the process.
Accordingly, the present invention provides an improved multi-lumen catheter and tip configurations for the simultaneous injection and withdrawal of fluids to and from a patient. The multi-lumen catheter of the present invention is preferably made of polyurethane and is a hollow, cylindrical structure. It includes an outer catheter, generally used for the intake of fluid from the body, and an inner catheter, generally used for injection of fluids into the body. The inner catheter is contained within the outer catheter and extends throughout its length. The hardness of the material used for the inner catheter and outer catheter can be varied, depending on the particular use of the catheter. The material used for the intake lumen should be harder to avoid lumen collapse due to suction, whereas the material used for the outflow lumen should be softer to alleviate trauma of the vein into which the catheter is inserted.
The inner catheter is bisected longitudinally by a septum, which creates two parallel lumens. The shape of each lumen is dependent on the shape of the septum, which can be widely varied. In the case that the inner catheter is split in half, the resulting two lumens are D-shaped. The inner catheter is secured by either the outer catheter""s tapered distal end, or a bond, wherein the bond secures the inner catheter to the outer catheter. In a preferred embodiment, the inner catheter extends beyond the distal end of the outer catheter to promote better differentiation between the intake fluid and the outflow fluid. In the case where the multi-lumen catheter is used for hemodialysis, the different lengths of outer and inner catheters help to keep the untreated blood and the purified blood separate. In addition, the two lumens contained within the inner catheter can be of different lengths to maintain fluid separation. The distal end of the two lumens contained within the inner catheter can be varied to improve reliability of fluid flow and avoid vein wall occlusions. For instance, the tips can be beveled, curved, slanted or otherwise altered so that occlusion is less likely. Further, side openings can be cut into either the outer catheter, the inner catheter, or both to improve the reliability of blood flow in the case that one of the lumens becomes occluded. Moreover, a mandrel could be inserted into one of the two lumens within the inner catheter, so that if one of the tubes did become occluded, the mandrel could be removed to provide an open pathway. The lumen could also accompany a guidewire for placement of the catheter.